1. Field of the Invention
The present invention relates to synchromesh mechanisms for transmissions and more particularly to the plate-or struct-type for automotive transmissions.
2. Description of the Prior Art
FIG. 1 shows a typical plate-type synchromesh mechanism 10 which consists of a hub 12, sleeve 14, plate 16, insert spring 18, blocking ring 20 and clutch gear 22. The hub 12 is splined to a transmission output shaft 28 and has external teeth. The sleeve 14 surrounds the hub 12 and has internal teeth meshing with the external hub teeth. Three plates or inserts 16 with a ridge running across the middle are centered in the sleeve 14 by a groove 14a around the inside center of the sleeve 14 and accommodated in the peripheral cuts 12a of the hub 12. A circular wire insert spring 18 is placed on each side of the hub 12 and holds the insert 16 outward so its ridge 16a engages the sleeve internal groove 14a, lightly holding the sleeve 14 centered over the hub 12. The outer edge of the sleeve 14 is provided with a groove 14b in which a shifting yoke, though not shown, fits. Changing gears is accomplished by sliding the sleeve 14 from its centered position on the hub 12 until the internal sleeve teeth engage the matching external teeth of the clutch gear 22. The clutch gear 22 is drivingly connected to an input gear 24 or 26 which is in turn connected through a drive clutch to an engine, though not shown in the drawing. The input gear 24 or 26 is rotatable on the output shaft 28 and will freewheel when the drive clutch disengages the engine. The blocking ring 20 is fitted between the sleeve 14 and the matching clutch gear teeth to prevent engagement until synchronization speed. The blocking ring 20 has a cone 20a that constitutes the external portion of a cone-type clutch. The clutch gear 22 has a matching tapered cone 22a that constitutes the internal portion of the cone clutch. The exterior of the blocking ring 20 has teeth that match the internal sleeve teeth and are chamfered at the sleeve side end. Similarly, the external clutch gear teeth are chamfered on the sleeve side. The blocking ring 20 is driven at hub speed by the three inserts 16 that fit into wide slots 20b provided to the hub side end portion of the blocking ring. The slots 20b are wide enough to allow the teeth to misalign by one-half a tooth in each direction.
During a gear shift, the drive clutch disengages the engine. A shifting yoke moves the hub 12 endwise toward the input gear 24 or 26 to be engaged. The insert ridge 16a moves the insert 16 endwise against the blocking ring 20 as the sleeve 14 moves. The insert 16 exerts a force against the blocking ring 20, engaging the cone clutch, i.e., the cones 20a and 22a. This, in turn, pulls the blocking ring 20 as far as the slots 20b will allow in the direction of relative rotation, causing a mismatch of the teeth which effectively blocks engagement while a speed difference exists. When the speeds of the clutch gear 24 or 26 and the sleeve 14 synchronize, the angle of the chamfered teeth causes a slight rotation that aligns the teeth and allows the sleeve 14 to engage the external clutch gear teeth.
In the above synchromesh mechanism, the capacity of the cone clutch should be large enough to assure positive synchronization action. The large capacity of the cone clutch inevitably requires the cones of the clutch to be large-sized either axially or radially, resulting in an increase in overall size of the transmission.